Proper operation of large screens for bulk products is essential for a cost efficient operation. A screen breakdown causes production loss and requires extensive repair. Therefore continuous monitoring of the screen operation is important to schedule preventive maintenance.
Under proper conditions, the movement of a screen is uniform from left to right sides. A good way to monitor the proper operation of a screen is therefore the installation of sensors at characteristic screen locations to measure and compare the three-dimensional movements of the screen continuously.
Screens can operate. with accelerations of up to 7 g, at frequencies of up to 25 Hz (1500 RPM) and can have amplitudes exceeding ¾″ (19.05 mm). This causes problems for the sensors, since standard sensors need to be connected to the data acquisition system with a cable containing typically 4 cores. This cable undergoes high repetitive flexing stress at the point where it is linked to the moving screen, which causes the cores to break quickly over time. Further. the sensors need to be connected to a power source, which also implies vulnerable cables. Accordingly, a method of powering devices located on the vibrating screen body is clearly needed to avoid that type of cabling. One possible solution to this problem is the use of an energy harvester. The purpose of the energy harvester is to convert the inherent movement of the vibrating screen into electrical energy in order to power electronic devices on or near vibrating screen bodies.
Energy harvesters which produce energy from vibrations are well described in the technical literature. WO 2010/0083746, for example, discloses an energy harvester to work with a swinging apparatus and a coil to generate an induced current for power generation during the swing of the swung mechanism. The natural frequency of the swing mechanism may be adjusted according to the rotational velocity of the energy provider.
There are, however, problems associated with the above technique and other prior art when used with vibrating equipment. Typical energy harvesters work best at or around one of their natural frequencies while the performance is significantly reduced or stopped as soon as the frequency deviates from these frequencies. If a resonant type energy harvester were to operate at the characteristic acceleration level of vibration equipment and feeders (3-7 g), the device would fail quickly or require extensive mechanical precautions to avoid destruction. Thus, energy harvesters available on the market are not capable of withstanding the high acceleration present or do not feature a suitably large operating bandwidth to accommodate the characteristics of vibrating equipment. Owing to the low acceleration applications, available energy harvesters are also not designed to supply large amounts of power.